Printed board assembly and method of its manufacture

ABSTRACT

A compact printed board assembly has a patterned copper-coated substrate ( 1 ) with electronic components ( 5, 12 ) mounted thereon. Depending on the height of the components, either SBU lacquer ( 11 ) or non-flow prepreg ( 3 ) and laminate ( 4 ) surround the electronic components. This subassembly is then sandwiched between two RC (resin coated) copper foils ( 8 ) with the resin ( 7 ) facing the components ( 5, 12 ) and burying them, thereby providing a new etchable copper surface which can be connected by means of microvias ( 10 ) to the embedded components ( 5, 12 ).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a printed board assembly, comprising acopper coated substrate with electronic components mounted thereon. Thesubstrate with components are sandwiched between resin coated foils thusembedding the components. The invention also relates to a method ofmanufacturing such a printed board assembly.

DESCRIPTION OF RELATED ART

EP 0 813 355 (A2) to International Business Machines Inc. relates to aprinted circuit board construction with stacked capacitive planes. Theentire stack is then covered with epoxy glass to which copper foil isthen applied. EP 0 813 355 (A2) does not provide for embedding anythingother than flat capacitive planes, having an etched outer surface towhich the epoxy adheres and bonds the copper foil.

Similarly, DE-A 196 34 016 (A1) to Taiyo Ink Mfg. Co. Ltd. describescoating a printed circuit board having circuit patterns etched thereinwith resin and laying a similar etched copper layer thereon which is inturn coated with resin. This reference, as that described above, doesnot describe anything other than the embedding of flat etched coppersheets.

SUMMARY OF THE INVENTION

A printed board assembly is provided comprising a substrate coated withan electrically conducting material, such as etched copper, electricalcomponents being mounted on said substrate, said substrate withcomponents being covered on both sides with resin coated conductingfoil, the resin of said resin coated foil facing the substrate andburying said components, said foil being etched with a circuit pattern,a non-conducting material being disposed in the areas between saidelectrical components.

The present invention enables more components to be packed morecompactly within and on the carrier, thereby making it possible toimprove the electrical performance, and to integrate the electricalshielding in the carrier. The mechanical stability and strength of theentire assembly is also improved.

According to one embodiment of the printed board assembly according tothe present invention, said components are chip resistors and that saidcarrier is coated between said chip resistors with a sequential built-up(SBU) lacquer. The lacquer is applied in the areas between the chipresistors sequentially until it reaches the level of the top surfaces ofthe chip resistors, whereupon the resin coated foil is easily applied tothe essentially flat surface. This is a very simple and low cost methodof integrating chip resistors into the carrier.

According to another embodiment of the printed board assembly accordingto the present invention said carrier is covered in the areas betweensaid components with a preimpregnated non-conducting resin mat orprepreg covered with a laminate, both provided with holes for saidcomponents. This enables the principle of the invention to be appliedwhen higher components than chip resistors are mounted on the substrate.There is either sufficient resin to fill out any remaining space betweenthese higher electronic components, or alternatively, these smallremaining spaces can be coated with SBU lacquer before the resin coatedfoil is applied thereon.

A method is also provided for manufacturing such a printed boardassembly, comprising the steps of: mounting electronic components on asubstrate patterned copper; covering only the areas of the copper coatedsubstrate between the mounted components with a non-conducting materialapproximately up to the level of the mounted components, sandwiching thesubstrate, components and non-conducting material between two sheets ofresin coated conducting foil, the resin on said foils facing thesubstrate and burying said components, and etching circuit patterns inthe exposed copper surfaces of the resin coated conducting foils. Thisis a very economical way of achieving vertical packing of manycomponents in a way which is advantageous structurally and electrically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a-e) show the sequence of steps in manufacturing a printed boardassembly of the present invention in accordance with one embodiment ofthe invention.

FIGS. 2(a-e) show the sequence of steps in manufacturing a printed boardassembly of the present invention in accordance with another embodimentof the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows the method of the present invention in a first embodimentstarting at step 1(a) with a standard copper coated 2 substrate 1. Instep 1(b), at least one of the copper coatings 2 on the substrate isetched in the known manner to provide a circuit pattern and then anon-conducting prepreg 3 and laminate 4, which have been machined tocreate holes for the areas where the electronic components are to bemounted, are pressed together with the substrate 1. The prepreg is aresin impregnated mat of “non-flow” type.

The electronic components 5, which in this case can be integratedcircuit components etc., are then mounted in the openings in the prepreg3 and laminate 4. This is shown in step 1(c).

The subassembly comprising the copper coated substrate 1, the prepreg 3and the laminate 4 are then sandwiched between two resin coated copperfoils 8 so that the resin 7 faces inwards. The result is shown in FIG.1(d).

It may be the case that the resin 7 does not fill the spaces under andaround the electronic components 5. In that case a lacquer, which may bean SBU (sequentially built-up) lacquer 9 is applied over the electroniccomponents. This variant is shown in FIG. 1(d′).

At least one of the foils 8 is then etched to form another printedcircuit layer and microvia holes 10 are made connecting the foil 8 layerto the electronic components. This assembly is shown in FIG. 1(e). It isa multi-layer assembly providing exceptional structural stability andcompact arrangement of many circuits. Heat can also be dissipatedthrough the via holes.

Another embodiment of the invention is shown in FIGS. 2(a-e) which showit applied to a printed board assembly which embeds only chip resistorsunder RC foil. The steps are essentially those described in relation tothe embodiments shown in FIGS. 1(a-e) and the corresponding componentshave been given the same reference numerals as in FIGS. 1(a-e), with theexception that the non-conducting material disposed in the areas betweenthe electrical components is only SBU lacquer. The prepreg and thelaminate used in the embodiments shown in FIGS. 1(a-e) are not necessarysince chip resistors are rather thin.

FIG. 2(a) shows a standard copper-coated substrate 1. A photosensitivedielectric material 11 is painted onto the copper 2 on one side, andopenings are made therein, (FIG. 2(b), into which chip resistors 12 aremounted (FIG. 2(c).

This subassembly is then sandwiched, as in the example above, betweentwo resin coated copper foils 8 so that the resin 7 faces inwards. Theresult is shown in FIG. 2(d).

As in the example above, at least one of the foils 8 is then etched toform a printed circuit layer and microvia holes 10 are made connectingthe chip resistors 12 with the foil layer 8. This assembly is shown inFIG. 2(e), which allows the chip resistors and other passive componentsto be embedded leaving space exposed on the upper layer for more activecomponents. The chip resistors 12 may also be contacted by soldering tothe patterned copper coating 2 on the substrate 1. This method providesgreat flexibility as regards contacting the components.

It is of course also possible to repeat the process and build up evenmore layers on top of the foil layer 8.

What is claimed is:
 1. Printed board assembly, comprising: a) asubstrate coated with an electrically conducting material, b) electricalcomponents mounted on some areas of said substrate, c) a non-conductingmaterial disposed in areas between said electrical components, and d) ametal foil pre-coated with resin on one side of said foil, wherein saidfoil covers both sides of said substrate including the electricalcomponents and the non-conducting material, wherein the resin of saidfoil faces the substrate and covers said electrical components such thatthe electrical components are buried under the resin, and said foil isetched with a circuit pattern.
 2. Printed board assembly according toclaim 1, wherein said electrical components are chip resistors and saidnon-conducting material is a sequential built-up (SBU) lacquer. 3.Printed board assembly according to claim 1, wherein said non-conductingmaterial comprises a preimpregnated non-conducting resin mat havingholes for said electrical components.
 4. Printed board assemblyaccording to claim 1, wherein said electrically conducting material ispatterned copper.
 5. Printed board assembly according to claim 1,wherein said non-conducting material comprises a prepreg covered with alaminate having holes for said electrical components.
 6. Printed boardassembly according to claim 1, wherein said non-conducting materialsubstantially reaches the level of the top of said electricalcomponents.
 7. Printed board assembly according to claim 1, wherein saidnon-conducting material is a preimpregnated non-conducting resin mathaving holes for said electrical components, said printed board assemblyfurther comprising another non-conducting material disposed in remainingspaces between said electrical components, said another non-conductingmaterial is a sequential built-up (SBU) lacquer.
 8. Printed boardassembly according to claim 1, wherein said non-conducting material is aprepreg covered with a laminate having holes for said electricalcomponents, said printed board assembly further comprising anothernon-conducting material disposed in remaining spaces between saidelectrical components, said another non-conducting material is asequential built-up (SBU) lacquer.
 9. The printed circuit board assemblyaccording to claim 8, further comprising microvia holes connecting thefoil to said electrical components.
 10. The printed circuit boardassembly according to claim 8, wherein said electrical conductingmaterial comprises etched copper.
 11. A printed circuit board assembly,comprising: a substrate coated with an electrically conducting material;electrical components mounted on said substrate; and, a metal foilpre-coated with resin on one side of said foil, wherein said foil coversboth sides of said substrate including the electrical components and anon-conducting material, the resin of said foil facing the substrate andcovering said electrical components, such that the electrical componentsare buried under the resin.
 12. The printed circuit board assemblyaccording to claim 11, wherein said non-conducting material comprises asequentially built-up (SBU) lacquer coating disposed in areas betweensaid electrical components.
 13. The printed circuit board assemblyaccording to claim 12, wherein said SBU lacquer substantially reachesthe level of the top of said electrical components.
 14. The printedcircuit board assembly according to claim 11, wherein said electricalcomponents are chip resistors.
 15. The printed circuit board assemblyaccording to claim 11, wherein said non-conducting material disposed inareas between said electrical components.
 16. The printed circuit boardassembly according to claim 15, wherein said non-conducting material isa preimpregnated non-conducting resin mat having holes for mounting saidelectrical components.
 17. The printed circuit board assembly accordingto claim 15, wherein said non-conducting material is a prepreg coveredwith a laminate having holes for mounting said electrical components.18. The printed circuit board assembly according to claim 15, whereinsaid non-conducting material also comprises a sequentially built-up(SBU) lacquer disposed in areas under and around said electricalcomponents not filled by the resin of said resin coated conducting foil.19. The printed circuit board assembly according to claim 11, whereinthe foil of said resin coated conducting foil being etched with acircuit pattern.